High brightness light sources have been proposed for a variety of centralized lighting applications whereby it is desired to have a single source of light which can be distributed to at least two locations remote from the light source. For instance, such a single light source, dual output arrangement could be put to beneficial use in the automotive industry for purposes of front end illumination. To this end, such a configuration has been proposed in U.S. Pat. Nos. 4,958,263 and 5,222,793 issued to Davenport et al on Sep. 18, 1990 and Jun. 29, 1993, respectively, and assigned to the same assignee as the present invention. Central source/remote light output configurations such as this could also be put to use in other applications such as in a merchandise display situation or for medical or scientific instrumentation. In some such applications, particularly automotive forward lighting arrangements, it would be desirable to have the light source exit from the dual ports which face in opposite directions from one another. As shown in FIG. 7 of the U.S. Pat. No. 5,222,793 referenced above, one approach would be to join two ellipsoidally shaped reflectors in a back-to-back configuration with the light source disposed approximately at the center of the point at which the reflector segments are joined. Although effective in achieving a dual light output which exits the source at oppositely facing directions to one another, this approach would require precision manufacturing and assembly operations to implement and accordingly, would result in a high priced end product. Therefore, it would be advantageous if a single source, dual output lighting arrangement could be achieved at a reasonable cost in terms of manufacturing of the component elements and the assembly thereof into a system configuration.
Another approach to providing a dual output from a single light source would be by use of a reflector and mirror arrangement such as shown in FIG. 3 of previously referenced U.S. Pat. No 5,222,793. In this arrangement, two optical fibers are disposed in close contacting relation to one another so that the light output from an ellipsoidally shaped reflector is reflected off a planar mirror surface and into the input faces of the contacting optical fibers. The lengths of optical fibers can then be arranged in a manner so as to achieve an effective separation of the light output to regions 180 degrees apart from each other. Although this approach is effective in splitting the light output so as to be conveyed to opposite sides of an automobile forward lighting system for instance, the manner by which this beam splitting is achieved results in a noticeable loss of light attributable to the fact that the shape of the input surface of the two side-by-side light guides does not match the output beam pattern and light is therefore lost around the edge of the side-by-side arrangement between the light guides. Additionally, because the space in which the optical fibers are routed is typically limited, it would be desirable to have the optical fibers exit the light source at an angle of separation between 90 and 180 degrees thereby avoiding bending of the optical fibers in order to achieve the separation to the two front end locations.
Furthermore, it would be advantageous if a light coupling arrangement could be achieved whereby light would enter the light guide or intermediate optical coupling member at a reduced angle relative to the longitudinal axis (i.e. transmission axis) of the light guide or optical coupler. By minimizing the entry angle into the light guide or optical coupler, less bouncing of light rays occurs within the light guide or optical coupler. Since each bouncing action results in a measurable light loss, such loss can be minimized by reducing the entry angle and hence reducing the number of light ray bounces within the light guide or optical coupler. Thus when the entry angles of the light rays are minimized, light transmission through the light guides is maximized.
In conjunction with the reduction of the entry angle, it would be further advantageous if a larger input surface area could be provided than would otherwise be attainable in certain centralized lighting systems. For instance, for an automotive forward lighting application, a 12 mm diameter light guide is typically utilized for transmitting light output from the light source to the two headlight locations. For a lighting system using a short arc gap light source and ellipsoidal reflector as described in U.S. Pat. No. 5,222,793, substantially all of the focused light is projected across a 19 mm diameter. Hence, a 12 mm light guide is ineffective for picking up light that occurs out to a 19 mm diameter round surface area. Therefore, it would be desirable to allow for collecting as much light as possible with a larger input surface area, yet still avoiding collection of such light over large entry angles.